1. Field of the Invention
The present invention relates to systems and methods for power combining high frequency electromagnetic signals. Particularly, this invention relates to efficient power combining of high power radio frequency (RF) signals in satellite applications.
2. Description of the Related Art
In many high power wireless communications systems, amplified signals are often combined in parallel to produce the high power output signals. For example, a satellite-based communication system may comprise a plurality of high power amplifiers such as traveling wave tube amplifiers (TWTAs) each amplifying the same RF signal. The respective output amplified RF signals from each TWTA are then combined in parallel to yield the high power broadcast RF signal that may be transmitted to Earth-based receivers. This technique of combining amplified signals is termed “power combining”.
One significant challenge in power combining signals arises from differences in phase among the combined signals. Even slight variations in the signal phase of the signals can negatively impact the overall power efficiency of the combined signals. In addition, phase variation among the signals also distorts the resulting combined signal. Such phase variation occurs as a consequence of slight differences in the amplifiers performance characteristics and the waveguide path lengths. Phase matching the signals becomes more difficult when higher frequency signals are used because wavelengths decrease and phase variation becomes more sensitive to line length variations. Thus, as more and more communication systems are developed for higher frequencies, the problem of phase matching becomes more prevalent. Accordingly, phase matching of power combined signals is often an objective in the design and production of systems using power combining.
Aligning multiple high power amplifiers to power combine efficiently is currently performed through a labor-intensive, manual procedure involving the use of mechanical waveguide shims to vary the path length of individual amplifier output ports. Adjusting the relative path lengths alters the relative phase of the combined signals. Thus, power combining efficiency is maximized through this shimming procedure. However, the shimming procedure yields a fixed result, tuning the power combiner to a single setting. The shimming procedure does not account for changes over the life of the system. Thus, differential variation among amplifier performance and waveguide characteristics occurring due to environmental (e.g. temperature) and other changes can greatly impact the power combining efficiency. For example, a conventional satellite-based communication system may be designed for a fifteen year mission during which the system is subject to a wide variety of environmental changes. Analyzing the phase misalignment and compensating with shimming becomes very costly and difficult (if not impossible) for systems employing phase sensitive power combining.
In view of the foregoing, the present invention provides a system and method for efficient phase matching power combined RF signals. In addition, embodiments of the present invention can be integrated into a satellite communications system to provide constant automatic phase adjustment between the power combined signals. These and other advantages of the present invention are detailed hereafter.